title: Skin temperature and heart rate can be used to estimate physiological strain during exercise in the heat in a cohort of fit and unfit males.
abstract: OBJECTIVE
  To evaluate the previously developed physiological strain index (PSI) model using heart rate and skin temperature to provide further insight into the detection and estimation of thermal and physiological heat strain indices. A secondary aim was to characterize individuals who excel in their performance in the heat.
  
  
  METHODS
  56 male participants completed 2 walking trials (3.5 miles per hour, 5% grade) in controlled environments of 43.3 °C and 15.5 °C (40% humidity). Core and skin temperature, along with heart rate and PSI, were continually monitored during exercise. Participants completed a physical fitness test.
  
  
  RESULTS
  The logistic regression model exhibited 4 false positives and 1 false negative at the 40% decision boundary. The "Not at Risk" group (N = 33) had higher body weight (84 ± 13 vs. 77 ± 10 kg, respectively) compared to the "At Risk" (N = 23) group, p < 0.05. The "Not at Risk" group had a faster 3-mile run time compared to the "At Risk" group (21:53 ± 3:13 vs. 25:16 ± 2:37, respectively), p < 0.05. During the Heat Trial, the "At Risk" group had a higher rating of perceived exertion at 60 and 90 minutes compared to the "Not at Risk" group (13.5 ± 2.8 vs. 11.5 ± 1.8 and 14.8 ± 3.2 vs. 12.2 ± 2.0 for "At Risk" vs. "Not at Risk" at 60 and 90 minutes, respectively), p < 0.05.
  
  
  CONCLUSIONS
  The previously developed model relating heart rate and skin temperature to PSI is highly accurate at assessing heat risk status. Participants classified as "At Risk" had lower physical performance scores and different body weights compared to the "Not at Risk" group and perceived themselves as working harder during exercise in the heat.
authors.affiliation: Montana Center for Work Physiology and Exercise Metabolism, The University of Montana, 32 Campus Drive, McGill Hall - HHP, Missoula, MT 59812, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Cuddy
authors.forename: Mark
authors.initials: M
authors.lastname: Buller
authors.forename: Walter S
authors.initials: WS
authors.lastname: Hailes
authors.forename: Brent C
authors.initials: BC
authors.lastname: Ruby
mesh_terms: D000328:Adult; D005080:Exercise Test; D005188:False Negative Reactions; D005189:False Positive Reactions; D006339:Heart Rate; D018882:Heat Stress Disorders / Q000175:diagnosis*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness; D012720:Severity of Illness Index; D012881:Skin Temperature; D016138:Walking / Q000502:physiology; D055815:Young Adult